Checked the tcp settings on my win7 machine, with several settings. No difference.
monitored iotop, and when the file uploads to OMV, I get multiple mhddfs streams (5-6 I believe) doing 3-4mb/sec. On the download, I get one stream running 110ish mb/s out of OMV to client

Am I missing something here? Any ideas? Moving around my 50tb video collection is going to take a HELLA long time at 20mb/s.

mergerfs with the direct_io flag can slow down reads. If you are doing lots of reading, don't set the flag. mergerfs was only part of the equation. You still need to find some other performance tuning parameters. Samba is obviously the limiting factor now.

ran iperf both ways in & out of the OMV box, and showed full Gbit transfer rates.

One thing that I found interesting is this:

- If I transfer files from my Win7 desktop to OMV, they transfer in the 15-20mb/s range
- If I transfer files from my WHS2011 machine to OMV, they transfer in the 10mb/s range
- If I transfer files from my Win7 desktop to OMV WHILE I am transferring files from WHS2011 to OMV, my desktop transfer rate goes up to 40mb/s range....

You still need to find some other performance tuning parameters. Samba is obviously the limiting factor now.

If you can't get the speeds you want, you need to tune samba. It can't possible be OMV's samba parameters when plenty of people can saturate gigabit without tuning parameters. So, it must be the clients configuration which samba can't account for. If that doesn't work, install samba4 from backports.